Due to supply voltage variations, the output current of a standard bias circuit deviates beyond required specifications. Hence a stable reference voltage is required for stable current output. A stable voltage may be generated externally and supplied to the bias circuit, which is applied in an amplifier component, for example. Such an external voltage supply is common use in industrial applications. Existing concepts are discussed in the paper 2001 IEEE MTT-S, “Bias circuits for GaAs HBT power amplifiers”, Esko, Jarvinen, pages 507-510.